The present invention relates to a magnetostatic wave band-pass-filter. In more detail, the present invention relates to a magnetostatic wave tunable band-pass-filter utilizing the ferromagnetic resonance of yttrium iron garnet (hereinafter referred to as "YIG"), and more particularly to a magnetostatic wave band-pass-filter having a planar structure with an electrode pattern formed, by photolithography, on a YIG film epitaxially grown on a gadolinium gallium garnet single crystal substrate (hereinafter referred to as "GGG substrate").
A conventional magnetostatic band-pass-filter utilizing ferromagnetic resonance of a YIG film is described in an article entitled "THE EFFECT OF THE WIDTH MODES ON THE PERFORMANCE OF MSSW RESONATORS" (IEEE Ultrasonics Symposium, 1984, pages 164 to 167). This band-pass-filter has the structure shown in FIGS. 9A and 9B of the accompanying drawings. That is, a YIG film 4 is grown on a single crystal GGG substrate 1 by liquid phase epitaxy. A chip resonator is cut out from the GGG substrate coated with the YIG film. An input microstrip electrode 3 and an output microstrip electrode 8 are formed on a microstrip substrate made up of a lower conductor 7 and a dielectric plate 13. The YIG film of the chip resonator is fixed to the microstrip substrate by an adhesive agent so that the distance between the input microstrip electrode and one of a pair of reflecting end faces of the YIG film is equal to the distance between the output microstrip electrode and the other reflecting straight edge of the YIG film. Incidentally, a band-elimination-filter (BEF) proposed by the present inventors and having a planar structure is disclosed in U.S. Pat. No. 4,743,874.